1. Field of the Invention
The present invention relates to an image-forming apparatus. More particularly, the present invention relates to an image-forming apparatus that has a developing unit that includes a toner pressure control device for preventing an increase in toner pressure in the developing unit.
2. Description of the Related Art
Generally, an image-forming apparatus prints a desired image on a recording medium by forming an electrostatic latent image on a photosensitive medium using an exposing unit, such as a laser scanning unit (LSU). The electrostatic latent image is developed into a toner image by using toner. The toner image is transferred and fixed on the recording medium by applying heat and pressure.
According to the type of toner and carrier used, image-forming apparatuses can be generally classified as either wet type apparatuses or dry type apparatuses. A dry type image forming apparatus can be further classified based on whether it has a one-phase developing device or a two-phase developing device.
An image forming apparatus that has a one-phase developing device forms an image by supplying only toner. In contrast, an image forming apparatus that has a two-phase developing device forms an image by supplying a mixture of toner and a carrier in which toner particles are adhered to the carrier.
An image-forming apparatus that has a one-phase developing device cleans any toner particles remaining on the surface of a photosensitive medium after developing a toner image thereon with a cleaning device, such as a cleaning blade. The toner particles are then reused in the next developing process.
An image-forming apparatus that has a two-phase developing device also reuses toner particles recovered from a surface of a photosensitive medium after developing a toner image thereon.
The above descriptions refer to black and white image formation. When forming a color image, however, toner remaining on the surface of a photosensitive medium cannot be reused since different color toners are mixed on the surface of the photosensitive medium.
To address this problem, an image-forming apparatus includes a developing unit that develops an electrostatic latent image into a toner image by supplying toner to the photosensitive medium on which the electrostatic latent image is formed. The developing unit receives toner from a toner storage space provided on the developing unit, or receives toner from a separate toner container that is connected to the developing unit.
The toner transferred to the developing unit is supplied to the photosensitive medium through a developing roller. When toner is continuously supplied to the developing unit and the developing unit is completely filled with toner, the toner pressure in the developing unit may increase. This may cause toner to leak from the developing unit and contaminate peripheral devices in the image-forming apparatus.
Therefore, there is a need for an image forming apparatus with a device that can prevent an increase in toner pressure in the developing unit by controlling the amount of toner supplied to the developing unit.